use dataloader to collect calls to DB fixes #30

lib/change-log.js

@@ -186,12 +186,12 @@ const _getChildChangeObjId = async function (
 const _formatCompositionContext = async function (changes, reqData) {
   const childNodeChanges = []
 
-  for (const change of changes) {
+  await Promise.all(changes.map(async (change) => {
     if (typeof change.valueChangedTo === "object") {
       if (!Array.isArray(change.valueChangedTo)) {
         change.valueChangedTo = [change.valueChangedTo]
       }
-      for (const childNodeChange of change.valueChangedTo) {
+      await Promise.all(change.valueChangedTo.map(async (childNodeChange) => {
         const curChange = Object.assign({}, change)
         const path = childNodeChange._path.split('/')
         const curNodePathVal = path.pop()
@@ -203,10 +203,10 @@ const _formatCompositionContext = async function (changes, reqData) {
           reqData
         )
         _formatCompositionValue(curChange, objId, childNodeChange, childNodeChanges)
-      }
+      }))
       change.valueChangedTo = undefined
     }
-  }
+  }))
   changes.push(...childNodeChanges)
 }
 
@@ -267,7 +267,7 @@ const _getObjectIdByPath = async function (
 
 const _formatObjectID = async function (changes, reqData) {
   const objectIdCache = new Map()
-  for (const change of changes) {
+  await Promise.all(changes.map(async (change) => {
     const path = change.serviceEntityPath.split('/')
     const curNodePathVal = path.pop()
     const parentNodePathVal = path.pop()
@@ -295,7 +295,7 @@ const _formatObjectID = async function (changes, reqData) {
     change.entityID = curNodeObjId
     change.parentEntityID = parentNodeObjId
     change.parentKey = getUUIDFromPathVal(parentNodePathVal)
-  }
+  }))
 }
 
 const _isCompositionContextPath = function (aPath, hasComp) {
@@ -309,6 +309,7 @@ const _isCompositionContextPath = function (aPath, hasComp) {
 }
 
 const _formatChangeLog = async function (changes, req) {
+  cds.context.dataloaders = {}
   await _formatObjectID(changes, req.data)
   await _formatAssociationContext(changes, req.data)
   await _formatCompositionContext(changes, req.data)

lib/entity-helper.js

@@ -1,4 +1,5 @@
 const cds = require("@sap/cds")
+const DataLoader = require("dataloader");
 const LOG = cds.log("change-log")
 
 
@@ -29,11 +30,21 @@ const getObjIdElementNamesInArray = function (elements) {
   else return []
 }
 
-const getCurObjFromDbQuery = async function (entityName, queryVal, /**optional*/ queryKey='ID') {
+const getCurObjFromDbQuery = async function (entityName, queryVal, /**optional*/ queryKey = 'ID') {
+  if (!(entityName in cds.context.dataloaders)) {
+    cds.context.dataloaders[entityName] = new DataLoader(async (keys) => {
+      // REVISIT: This always reads all elements -> should read required ones only!
+      const results = await SELECT.from(entityName).where(queryKey, 'in', keys)
+      const resultsByKey = results.reduce((acc, instance) => {
+        const key = instance[queryKey]
+        acc[key] = instance
+        return acc
+      }, {})
+      return keys.map(key => resultsByKey[key] || {})
+    })
+  }
   if (!queryVal) return {}
-  // REVISIT: This always reads all elements -> should read required ones only!
-  const obj = await SELECT.one.from(entityName).where({[queryKey]: queryVal})
-  return obj || {}
+  return cds.context.dataloaders[entityName].load(queryVal)
 }
 
 const getCurObjFromReqData = function (reqData, nodePathVal, pathVal) {

package.json

@@ -37,5 +37,8 @@
         "model": "@cap-js/change-tracking"
       }
     }
+  },
+  "dependencies": {
+    "dataloader": "^2.2.2"
   }
 }

tests/integration/fiori-draft-enabled.test.js

@@ -1,6 +1,7 @@
 const cds = require("@sap/cds");
 const bookshop = require("path").resolve(__dirname, "./../bookshop");
 const { expect, data, POST, PATCH, DELETE } = cds.test(bookshop);
+const { expect: jestExpect } = require('@jest/globals');
 const { RequestSend } = require("../utils/api");
 
 jest.setTimeout(5 * 60 * 1000);
@@ -1569,4 +1570,50 @@ describe("change log integration test", () => {
         expect(changeLogs[0].entityKey).to.equal("5ab2a87b-3a56-4d97-a697-7af72334a384");
         expect(changeLogs[0].serviceEntity).to.equal("AdminService.BookStores");
     });
+
+    it("Issues-30 Should only optimize reads to the DB", async () => {
+        const action1 = POST.bind(
+            {},
+            `/odata/v4/admin/BookStores(ID=64625905-c234-4d0d-9bc1-283ee8946770,IsActiveEntity=false)/books`,
+            {
+                ID: "9d703c23-54a8-4eff-81c1-cdce6b8376b2",
+                title: "test title 1",
+                descr: "test descr",
+                author_ID: "d4d4a1b3-5b83-4814-8a20-f039af6f0387",
+                stock: 1,
+                price: 1.0,
+                isUsed: true
+            }
+        );
+        const action2 = POST.bind(
+            {},
+            `/odata/v4/admin/BookStores(ID=64625905-c234-4d0d-9bc1-283ee8946770,IsActiveEntity=false)/books`,
+            {
+                ID: "3e53bf3b-53f7-4db8-87ce-8bb0818574d8",
+                title: "test title 2",
+                descr: "test descr",
+                author_ID: "d4d4a1b3-5b83-4814-8a20-f039af6f0387",
+                stock: 1,
+                price: 1.0,
+                isUsed: true
+            }
+        );
+        const cdsRunSpy = jest.spyOn(cds.db, "run");
+        await utils.apiAction("admin", "BookStores", "64625905-c234-4d0d-9bc1-283ee8946770", "AdminService", [action1, action2]);
+        jestExpect(cdsRunSpy).toHaveBeenCalledWith(jestExpect.objectContaining({
+            SELECT: jestExpect.objectContaining({
+                from: jestExpect.objectContaining({ ref: ["AdminService.Books"] }),
+                where: jestExpect.arrayContaining([
+                    jestExpect.objectContaining({ ref: ["ID"] }),
+                    "in",
+                    {
+                        list: [
+                            { val: "9d703c23-54a8-4eff-81c1-cdce6b8376b2" },
+                            { val: "3e53bf3b-53f7-4db8-87ce-8bb0818574d8" }
+                        ]
+                    }
+                ])
+            })
+        }));
+    });
 });

tests/utils/api.js

@@ -8,7 +8,13 @@ class RequestSend {
                 PreserveChanges: true,
             });
         }
-        await action();
+        if (Array.isArray(action)) {
+            for (const act of action) {
+                await act();
+            }
+        } else {
+            await action();
+        }
         await this.post(`/odata/v4/${serviceName}/${entityName}(ID=${id},IsActiveEntity=false)/${path}.draftPrepare`, {
             SideEffectsQualifier: "",
         });